This application claims the priority of German patent document 19944183.9, filed Sep. 15, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a hydraulic shock absorber for motor vehicles. Preferred embodiments of the invention relate to a hydraulic shock absorber for motor vehicles comprisisng a fluid-filled cylinder in which a piston rod is immersed on one side with a main piston which displaceably separates two working chambers from one another inside the cylinder with fluid exchange, with the main piston bearing an auxiliary piston which enters an auxiliary cylinder fixed axially in the cylinder at the end of the immersion movement of the main piston, with the inlet opening of said auxiliary cylinder leading to a fluid-filled chamber with a volume that varies as a function of spring force and the pressure increase linked therewith when the inlet opening is sealed by the auxiliary piston in the working chamber associated with the auxiliary piston causes a valve to open that produces a connection from this working chamber to the fluid-filled chamber.
A shock absorber of this type is known from German Patent Document DE 40 28 785 A1. According to this document, the shock absorber consists of a fluid-filled cylinder in which a piston rod with a main piston is immersed on one side. This separates the interior of the cylinder into two working chambers. To produce the damping effect, through bores are provided on the main piston through which a fluid exchange takes place between the two working chambers as the main piston moves. The main piston carries an auxiliary piston which enters a fixed auxiliary cylinder at the end of the immersion movement of the main piston. A gap opening between the auxiliary piston and the auxiliary cylinder is designed so that it narrows as the depth of penetration of the auxiliary piston increases, and thus produces an increasing damping effect. The inlet opening on the auxiliary cylinder leads to a fluid-filled chamber with a volume that varies against spring force. With the inlet opening sealed by the auxiliary piston, the pressure increase associated therewith in the working chamber associated with the auxiliary piston causes a valve to open that produces a connection between this working chamber and the fluid-filled chamber.
With such a design for a hydraulic shock absorber, the degree of damping in the compression stage becomes much greater. The degree of damping in the suction stage is constant regardless of the damping travel.
A goal of the invention is to improve on a hydraulic shock absorber of the above noted type so that the shock absorber produces a travel-dependent damping effect in the suction stage as well.
This goal is achieved according to the invention by providing a hydraulic shock absorber of the above-noted type, wherein the fluid exchange between the two working chambers of the cylinder takes place through a connection of the two working chambers which extends through the auxiliary piston and whose opening cross section to the working chamber is reduced by pushing the auxiliary piston into the auxiliary cylinder.
Advantageous features of preferred embodiments of the invention are described below and in the claims.
According to the invention, a hydraulic shock absorber for motor vehicles consists of a fluid-filled cylinder in which a piston rod with a main piston is submerged on one side. The piston displaceably separates two working chambers within the cylinder with fluid exchange, with the main piston carrying an auxiliary piston which at the end of the immersion movement of the main piston enters an auxiliary cylinder mounted axially in the cylinder whose inlet opening leads to a fluid-filled chamber with a volume variable against spring force. When the inlet opening is closed by the auxiliary piston, the pressure increase associated therewith in the working chamber associated with the auxiliary piston causes a valve to open, producing a connection between this working chamber and the fluid-filled chamber. The invention is characterized by the fact that fluid exchange between the two working chambers of the cylinder occurs through at least one connection between the two working chambers that runs through the auxiliary piston and whose opening cross section to the working chamber is reduced by pushing the auxiliary piston into the auxiliary cylinder.
A hydraulic shock absorber thus designed damps increasingly softly in the suction stage as the extension increases. In the compression stage, damping takes place by the fluid exchange between the two working chambers of the cylinder through the connection between the two working chambers that runs through the auxiliary piston, continuously over the compression distance.
One embodiment of the subject of the invention is characterized by the fact that the connection of the two working chambers runs through the auxiliary piston and through the piston rod, with the latter abutting one another in the axial direction, being made hollow, and having at least one opening each in the radial direction to the corresponding working chamber. The opening of the auxiliary piston to the working chamber is designed so that it is sealed by the auxiliary cylinder during an immersion movement of the auxiliary piston into the auxiliary cylinder.
Such a design of the subject of the invention is advantageously easy to make.
According to another feature of preferred embodiments of the subject of the invention, the auxiliary piston has a plurality of radially directed openings to the working chamber associated therewith, said openings being arranged in the axial direction so that they are closed in succession when the auxiliary piston is immersed in the inlet opening. This has the advantage that the openings in the auxiliary piston can be mounted very simply and precisely, for example as bores of different sizes with regular or irregular axial distances from one another as required for the desired influence of the damping behavior of the shock absorber.
Another advantage of the invention can be considered to be the fact that the kinematic steering systems that are conventional today are no longer necessary when a telescopic shock absorber is articulated to a rear wheel roller by using a damper according to the invention. Maintenance- and wear-intensive parts with bearings on a motorcycle chassis are reduced considerably thereby.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.